Preference for different inorganic-nitrogen forms among plant-functional types and species of the Patagonian steppe

GHERARDI, LAUREANO; OSVALDO E. SALA; LAURA YAHDJIAN

OECOLOGIA

SPRINGER

Lugar: Berlin; Año: 2013 vol. 173 p. 1075 - 1081

0029-8549

We explored species-specific preferences for nitrate and ammonium as an alternative niche separation in ecosystems where nitrogen (N) is mostly inorganic. The Patagonian steppe is dominated by shrubs and grasses. Shrubs absorb water and nutrients from deep soil layers, which are N poor, while grasses have the opposite pattern. We hypothesized that shrub and grass preferences for inorganic-N forms are different, and that the rate of potential N-uptake is greater in shrubs than in grasses. We hydroponically grew individuals of six dominant species in solutions with different ammonium:nitrate concentration ratios. Nitrate uptake was higher in shrubs, while ammonium uptake was similar between plant-functional types. The NH4+:NO3- uptake ratio was significantly lower for shrubs than grasses showing opposite preference for different N forms. Shrubs, which under field conditions have deeper rooting systems than grasses, showed higher N-absorption capacity than grasses and preference for the more mobile N-form, nitrate. Grasses preferred ammonium over nitrate and have lower N-uptake rates than shrubs. These complementarities between grasses and shrubs suggest a more thorough exploitation of resources by diverse ecosystems than those dominated by just one functional type. Loss of one group or a significant change in its abundance would represent a reduction in resource-use efficiency and ecosystem functioning.